The “Unassailable” Molyneux a fallacy by Chris Cantwell

The structure of Molyneux’s proof (proof by contradiction):

Prove murder (aggression in general) cannot be universally preferrable (the statement P).

assumptions and definitions (all are true by default):

  1. assumption (since Molyneux doesnt define ALL aggression/murder requires that the victim does not desire the act itself. assumed as part of the criteria of the definition. (point of contention)

2. preferable: (p.33 UPB) Thus when I talk about universal preferences, I am talking about what people should prefer, not what they always do prefer. To use a scientific analogy, to truly understand the universe, people should use the – 34 – scientific method – this does not mean that they always do so, since clearly billions of people consult ancient fairy tales rather than modern science for “answers.” There is no way to achieve truth about the universe without science, but people are perfectly free to redefine “truth” as “error,” and content themselves with mystical nonsense.

3. theorem: “can” is a necessary but not sufficient condition for “to do” (no proof necessary, trivial proof)

again molyneux is essentially going against his definition of a normative (should) definition of preferable and instead proceeding with a positive definition (what they actually do prefer) to complete his proof. which is a substantial error in his proof which i will elaborate on in my future video with the complete. not only that but his choice of terms in particular (preferable) contains the suffix “able”.  this is a “CAN”, not a “should” or a “is”

but let set that MAJOR error aside for not to explore if there is another error.  we shall allow Molyneux to redefine universally preferable to mean what the two people in hypothetical room actually do prefer.

since 3. the objective of molyneux is to show they cant both prefer murder. because if a necessary condition isnt present, then that is sufficient to guarantee that is not preferred.  therefore it would be universally preferable (really preferred,under the new positive definition)

so his proof, at least as presented by cantwell, is proof by contradiction.

since the goal is to prove murder/aggression is not UPB.  we assume the opposite of what molyneux set out to prove.  namely “murder/aggression is preferable” or more literally by the conflated positive definition “murder aggression is preferred”

but by 1. (the assumption that the aggression/murder require the victims non-preference) then this necessarily leads to the contradiction the victim both prefers and does not prefer murder/aggession.

since this leads to a contradiction the assumption “murder/aggression is preferable” must be false (proof by elimination, if the truth value of a statement is false then its negation must be true)

the problem with 1. is that one can construct a counterexample.


molyneux commits induction fallacy or black swan fallacy. the fact that a person’s experiences have yet to contradict a belief, so he believes it to be a universal absolute.  this is not valid logic.  one must deductively show by analysis of the definition that the entire set under consideration (in this case humans) must abide by this belief.




Molyneux’s proof:

let P= “murder/aggression is not UPB”

then ~P= “murder/aggresion is  UPB”

let Q = “the victim of the murder prefers murder”

then ~Q = “the victim of the murder does not prefer murder”

assume ~P

from 1,

we have the contradiction Q and ~Q

therefore P



my proof:

let A= the set of aggression

let P= “A is never preferred by the victim”

therefore ~P = “there exists an element “a” of A that”

consider a=








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